Rock sampling

ABSTRACT

A method for sampling rock and other brittle materials and for controlling resultant particle sizes is described. The method involves cutting grooves in the rock surface to provide a grouping of parallel ridges and subsequently machining the ridges to provide a powder specimen. The machining step may comprise milling, drilling, lathe cutting or the like; but a planing step is advantageous. Control of the particle size distribution is effected primarily by changing the height and width of these ridges. This control exceeds that obtainable by conventional grinding.

United States Patent [72] Inventor Philip Blum Lexington, Mass.

[21] Appl. No, 857,241

[22] Filed Sept. 11, 1969 [45] Patented Oct. 12, 1971 [7 3] AssigneeNational Research Corporation Cambridge, Mass.

Continuation-impart of application Ser. No. 611,414, Jan. 24, l 967, nowabandoned.

[54] ROCK SAMPLING 10 Claims, 9 Drawing Figs.

[52] US. Cl 125/1,

125/3, 299/86, 51/283 [51] Int. Cl B28d l/00 [50] Field of Search175/58,

[56] References Cited UNITED STATES PATENTS 1,496,522 6/1924 Canning125/3 UX 1,580,155 4/1926 Niestradt.... 125/4 2,718,732 9/1955 Comstock51/47 3,123,157 3/1964 Graham. 175/58 3,374,034 3/1968 Conner 299/86Primary Examiner-Harold D. Whitehead Att0rneysl(enneth W. Brown, ArthurS. Collins, Barry R.

Blaker and Lawrence A. Chaletsky ABSTRACT: A method for sampling rockand other brittle materials and for controlling resultant particle sizesis described. The method involves cutting grooves in the rock surface toprovide a grouping of parallel ridges and subsequently machining theridges to provide a powder specimen. The machining step may comprisemilling, drilling, lathe cutting or the like; but a planing step isadvantageous. Control of the particle size distribution is effectedprimarily by changing the height and width of these ridges. This controlexceeds that obtainable by conventional grinding.

6 WEIGHT PER CATEGORY PATENTED 0m 1 2 I971 PARTICLE SIZE (IN MIGRONSIFIG.2

SHEET 1 [IF 3 I6 WEIGHT PER CATEGORY FIG.3

PARTICLE SIZE (IN MICRONS) ATENTED am 1 2 mm 3,612,030

SHEU 2 [1F 3 ROCK FIG. IC

ROCK SAMPLING This application is a continuation-in-part of Ser. No.611,414 filed Jan. 24, 1967 and now abandoned. An additional relatedapplication is Ser. No. 768,942 filed Aug. 6, 1968, a division of saidSer. No. 61 1,414.

The invention described herein was made in the performance of work undera NASA contract and is subject to the provisions of the NationalAeronautics and Space Act of 1958, Public Law 85568 (72 Stat. 426; 42U.S.C. 2451) as amended. A license has been granted to the United StatesGovernment for practice of the invention and title to the invention andthis patent has been reserved to the assignee, subject to voidability byNASA.

There is a need in geological sampling for an apparatus which willabrade a rock surface and give high yields in particular particle sizeranges without requiring subsequent classification or sievingtechniques. An important reason is that minerals ordinarily fragmentinto unique size distributions and classification may therefore altertheir representation in the powder specimens.

It has been discovered that known grinding techniques do not affordadequate particle yields between 75 and 150 microns, a range suitablefor analysis by a petrographic microscope. Conventional grinding, e.g.,of basalt, tends to produce fine particles with sizes predominantlybelow 44 microns. Variation of conventional grinding parameters such aswheel speed and grit size does little to increase the yield above thisrange or to change the'shape of the size distribution curve.

The present invention gives a two-step treatment to rock or otherbrittle material. This consists in cutting a series of ad jacent grooveson the surface of the brittle material to form a grouping of parallelridges. The ridges are subsequently.

machined by a toothed machining process, preferably by planing. Controlover particle size distribution is effected by altering the thicknessand height of these ridges, aswell as by altering machining parameters,such as depth of cut, degree of tooth sharpness, axial and radial rake,wheel speed and traverse speed.

The use of the invention is now described with reference to theaccompanying drawings wherein:

FIG. 1 is a schematic sketch of an improved sampling apparatus;

FIG. 1A is a diagram showing a variation of the ridge cutter and FIGS.IB and IC show other variations of the apparatus;

FIG. 2 is a bar graph showing size distribution of rock particlesobtained using prior art grinding techniques;

FIG. 3 is a bar graph showing the improved distribution obtained in oneexample of use of the present invention;

FIGS. 4 and 5 are sketches of other embodiments of the apparatus; and

FIG. 5A is a plan view of a ridged surface being machined by a toothcutter and indicating axial rake angle.

Referring to FIG. 1 there is shown a rock to be sampled, a tool carriage12 traversing in the path and direction indicated by the arrow 14.Mounted on the carriage are a group of thin diamond grinding wheels 18and a milling cutter 20 with wedge-shaped teeth. The wheels 18 andmiller 20 are driven by a motor (not shown) mounted in the carriage 12.The wheels 18 cut closely spaced parallel grooves 22 thus fonning ridges24. The milling cutter cuts the ridges down partially (but not fully) toproduce a more controllable yield in terms of particle size. Only themilled powder is collected. A collection cup (not shown) is mounted onthe apparatus for this purpose.

FIG. 1A shows a variation of the apparatus in which a single wheel withseveral parallel lands 114 is used instead of several grinding wheels.It should be noted that here the rock sample 110 has a narrow profile.The profile should preferably be preground (by the wheel 118 withabrasive on the flats 119 or a separate grinder) to the level 111 toprovide a common level for groove and ridge formation.

F 10. 1B shows a variation of the apparatus formed as a rock drill fortaking a sample in a predrilled hole. A wheel 118 (similar to the wheel118 of FIG. 1A) and a milling cutter 120 are mounted on a common shaft115. They are driven from support 114 for traversing on the same rotarypath and they are individually rotated by gears 130.

FIG. 1C shows another version of the apparatus on a pendulum mount withcutoff wheels I18 and a milling cutter 120 and collection boxes 226. Thewheels I18 and 120 again travel the same path and same direction. Thewheel drive transmission is not shown.

The pendulum continually swings around with the cutoff wheel 118lowering the rock contour until a suitable level is obtained. Then themilling cutter collects a sample for use in analytical processes.

FIG. 2 is a bargraph showing the highest yield of particles in and aboutthe 74-149-micron range obtained by conventional grinding of basalt.(The particle sizes indicated on the abscissa between 0 and w are thesieve sizes used.) The distribution shown was obtained by traversing therock at 12 inches per minute, using a l6-grit diamond wheel run at 440revolutions per minute, and taking off 0.005 inch of rock per traverse.

FIG. 3 shows the improved sample distribution obtained from the samerock using the method of the present invention. Besides the improvementin immediate range of interest, which is shown shaded, here is a sizableincrease in the adjacent 149-250-micron range and a marked reduction inthe under 44-micron range. Further peaking of the distribution about thedesired 74-l49-micron range can be obtained with further adjustment ofridge widths and heights as described below. The results shown in FIG. 3were obtained using the following conditions: The previously describedgrooves were cut with a 60-mil width and 35-mil depth producingintervening ridges of I5-mil width and 35-mil height. The preparedsurface was traversed by a flat tooth milling cutter rotating at 440revolutions per minute and traversing at 30 inches per minute. Themilling cutter took 0.008 inch off the ridges per traverse.

The reasons for the size control using the present invention are thefollowing: The production of grooves removes considerable support fromthe remaining ridge material. As a result a reduction is effected in theamount of mechanical crushing pressure required to remove the ridgematerial.

Fewer fines are thereby produced because the amount of material whosecohesive force exceeds the disruptive comminution force increases. Forthis reason, within limits, the thinner the ridges, the fewer the numberof resultant fines. Imposition of an upper particle size limit is alsoassisted. The latter results from limiting particle size in onedimension, that provided by the ridge width. Advantageous results havebeen obtained with ridge widths many times greater than the' desiredparticle size but optimal results should occur with ridge widthapproximately equal to the desired size. Ridge height should be greaterthan the particle size desired, optimally about double. However,advantageous results have been obtained with heights many times larger.Depth of cut should be less than the ridge height and, optimally, aboutequal to the desired particle size.

The toothed-machining should utilize an axial rake angle greater than 0.The radial rake angle should preferably be negative for planing andpositive for milling. The edge of the cutting tooth should be dullrather than sharp. It was found desirable to run a fine-grit diamondwheel over a tungsten carbide tooth to wear away its freshly sharpenededge.

In the preliminary grinding to produce ridges, avoidance of heat wasfound desirable to avoid simultaneous ridge fracture. For quickest ridgeproduction compatible with minimal fracture, a 7-inch wheel usingl20-grit diamond abrasive with a medium strength bond was run at 400revolutions per minute. Equivalent surface feet per minute should beutilized in other wheel sizes. Traverse rates must also be low, about0.5 inch per minute. These conditions worked well with diverse rockcompositions.

FIG. 4 shows a drill form of rock-sampling apparatus using a planingtool. The ridges are produced by cutting grooves with alternately placedsemicircular core drills 418. This arrange ment avoids problems of ridgepinching which attend use of completely circular concentric core drills.The groove cutters are followed up by a planing tool 420. The drillassembly moves in the rotary direction 402 for grinding and scraping.Gas pressure is used to separately flush out undesired groove posed tothe zero rake angle of 520' shown in dashed lines as an alternativeconfiguration).

Selected results of sampling experiments are tabulated in table I below.The results indicate the improvemen in reduc- 5 tion of fines and inbetter distribution obtained through the present invention compared toconventional grinding. The results also show the distinctly advantageouscharacter of the planing species over the milling species.

TABLE I Variables Ridgr Depth Powder weight distribution size d of cut.3 (percent per micron sicvc interval) A xial l'or CE 20- 4+ 74- 149-250- 420 841- AM 1 Rock rako, Wd Ht. pass Total percent 20 44 74 1-10250 420 841 m I .7 2') 15 O 1O 5 II li 45 H K 5 35 5 7.[) 30 El .20 11)37 i4 1 1 1 II l3 0 8 4 4. 5 4, 'v 72 13 2-) 11 30 20 2 1 1 II" B 45 S R4. 5 4. 5 81! 15 18 1'7 6 3 2 ll... O 45 8 X 4.5 4.5 7H 4 17 13 23 27 i32 1 il l l5 0 l0 l5 l0. 0 .10. I) 85 5 1H 10 17 P2 22 4 0 IV B 5.0 5.69U 17 -11 12 14 ll 3 l Abrasion Method (AM): I-Desircd distribution llPlnnning IIIMiIIing iY Convcntionnl grinding.

3 In mils.

' Collection EIIicir-ncy (PE).

5 Some cutter flcxm'c.

cuttings and desired ridge scrapings. Unground rock surface is indicatedat 499, a ridge before scraping is shown at 498 and a residual ridgeafter scraping is shown at 497.

FIG. 5 shows another apparatus for ridge cutting and machining using aplaning-type maching tool. A shaft 514 is supported from a carrier 510(e.g. a spacecraft) and has mounted at its end a ganged set of grindingwheels 518 and a planing tool 520. The tools 518, 520 are moved along acircular traverse path 501 initially in direction 502 for cutting andthen in direction 503 for retrace and powder collection. Also includedin the apparatus is a collection box 526.

The shaft 514 is adjustable to act as an adjustable radius of thecircular path 501 to ensure tangential contact with rock to be sampledand permitting hunting for solid rock, removal of overlying powder andfinally sampling of powder in accordance with the present method anddelivery to the spacecraft.

The edge of scraper 5 is located on an arc radius smaller than that ofthe grinding wheels S18. Changes in radius of are 501 determine totalridge height and depth planed (scraped) per pass while the differentialradius between 520 and 518 determines residual ridge height afterplaning, which is invariant with the number of passes.

Acquisition of rock samples is independent of rock contour andrepetitive. Prelevelling of rock surface is not necessary.

Moving in direction 505: the apparatus cuTs grooves and planes toproduce powder which is thrown down on the ridged rock surface and intothe trenches due to the negative radial rake angle R of tool 520. On thereturn pass, moving in direction 503, the grinding wheels tend to throwthe powder in a shallow direction indicated by arrow B into box 526. Onthe next cutting pass, however, new trench cuttings tend to be thrown asshown in arrow A and avoid collection.

FIG. 5A indicates a axial rake angle for tool 520 (as op- Sevcralvariations can be made from the above-described 0 embodiments. it istherefore intended that the above disclosure shall be read asillustrative and not in a limiting sense.

lclaim: 1. Method of producing a sample of brittle material withcontrolled particle size comprising the steps of grinding paral- 35 lelgrooves in a surface of the brittle material to form interveningparallel ridges and subsequently machining these ridges with a toothedcutter to remove portions of the ridges whereby more particles of thedesired size are obtainable than by convcntional grinding alone.

2. The method of claim I wherein the ridges are produced in a widthabout equal to the desired average particle diameter.

3. The method of claim 1 wherein the tooth machining step is carried outas a planing type of cutting.

4. The method of claim 1 wherein the tooth machining step is carried outas a rotary type of cutting.

5. The method of claim 1 wherein the depth of tooth cut is about equalto the desired particle size.

6. The method of claim 1 wherein the toothed cut is carried out at anegative radial rake angle and the machining step is carried out as aplaning type of cutting.

7. The method of claim 1 wherein adjacent ridges to be cut are producedin sequence rather than simultaneously.

8. The method of claim 1 wherein the grinding means are retraced over amachined region to move powder for collection purposes.

9. The method of claim 1 further comprising traversing the groovecutting and machining means in tandem using a common drive.

10. The method of claim 9 further comprising supporting the groovecutting and machining means on a common radial mount and adjusting themount in radial length to hunt the surface of the brittle material.

1. Method of producing a sample of brittle material with controlledparticle size comprising the steps of grinding parallel grooves in asurface of the brittle material to form intervening parallel ridges andsubsequently machining these ridges with a toothed cutter to removeportions of the ridges whereby more particles of the desired size areobtainable than by conventional grinding alone.
 2. The method of claim 1wherein the ridges are produced in a width about equal to the desiredaverage particle diameter.
 3. The method of claim 1 wherein the toothmachining step is carried out as a planing type of cutting.
 4. Themethod of claim 1 wherein the tooth machining step is carried out as arotary type of cutting.
 5. The method of claim 1 wherein the depth oftooth cut is about equal to the desired particle size.
 6. The method ofclaim 1 wherein the toothed cut is carried out at a negative radial rakeangle and the machining step is carried out as a planing type ofcutting.
 7. The method of claim 1 wherein adjacent ridges to be cut areproduced in sequence rather than simultaneously.
 8. The method of claim1 wherein the grinding means are retraced over a machined region to movepowder for collection purposes.
 9. The method of claim 1 furthercomprising traversing the groove cutting and machining means in tandemusing a common drive.
 10. The method of claim 9 further comprisingsupporting the groove cutting and machining means on a common radialmount and adjusting the mount in radial length to hunt the surface ofthe brittle material.